Touch Screens/Transcript
Transcript Text reads: The Mysteries of Life with Tim and Moby Tim and Moby are at an electronics store. Moby repeatedly taps the screen of a smartphone that is on display. There is a metal clank each time his finger hits the screen. A salesperson looks on disapprovingly, her hands on her hips. TIM: You're gonna break it. The salesperson pointedly clears her throat. TIM: Sorry. He's, uh, from out of town. Tim's own cell phone vibrates. He removes it from his pocket and looks at its screen. A new e-mail has arrived. He touches his screen to open the e-mail, then reads it aloud. TIM: Dear Tim and Moby, Why doesn't my phone work when I have gloves on? Thanks, Evan. Hey, Evan. Most touch screens rely on the fact that people are filled with ions. That's any particle that carries a positive or negative charge. An animation shows a young girl touching her smartphone with her fingertips. A second animation depicts the ions going from the young girl into her phone. TIM: Ions course through all our body fluids, blood, sweat, stuff like that. MOBY: Beep. TIM: Their electric charge is useful for all sorts of functions. They carry signals through our nerves, maintain the fluid balance in our cells, and even keep our hearts beating. An animation shows an ion-filled silhouette of an adult. Smaller animations show a nerve cell, a skin cell, and a beating heart. TIM: They also react to charged objects outside of our bodies. MOBY: Beep. TIM: Exactly: like the screen on a smartphone or tablet. That's how they sense your touch. Tim picks up a smartphone. He touches its screen, and an animation shows the movement of the ions on his finger. TIM: This type of screen, used in most mobile devices, is called capacitive. MOBY: Beep. TIM: Well, because they function like capacitors. Open any electronic device, and you'll see them. They're often shaped like M and M’s, or tiny soda cans. An animation shows the inside of a handheld game unit. It contains capacitors. Images show the types of capacitors that Tim describes. TIM: These little guys are super useful, because they can store and release electricity. MOBY: Beep. TIM: Right. All electric circuits run on current: a stream of electrons. Commonly known as electricity. An animation shows a moving line of electrons, representing a current. TIM: Like in a lamp: turn it on, and electric current flows into the bulb. The animation shows an electric circuit running between a battery and a light bulb. TIM: But most devices are more complicated than that. They need to stop, start, and alter the current. An animation shows a microcircuit board, routing current in a more complicated way than the battery-and-light bulb model. TIM: That's where capacitors come in handy. MOBY: Beep. TIM: There are lots of different kinds, but their basic setup is the same. They contain an insulator, a material that blocks current. It's sandwiched between two conductors, materials that transmit current. An animation shows a capacitor and its insulator and conductors. TIM: When a current flows into one end of a capacitor, it gets stuck. It can't jump across the insulator and keep moving. So, the electrons build up, creating a negative charge. An animation shows current going into a capacitor, but not coming out. The electrons build up in one part of the capacitor. MOBY: Beep. TIM: With any electric charge, you get a field, an invisible area of force. This field passes right through the insulator, to the other conductor. The animation shows the field created by the stored electrons, as Tim describes. TIM: Since it's negative, it pushes away electrons. Because like charges repel each other. That gives the other conductor a positive charge. Its positive field attracts even more electrons to the first conductor, so it gets an even bigger buildup in charge. The animation demonstrates the process Tim describes. MOBY: Beep. TIM: Eventually, the electrons are given a path to the other conductor. This discharge can happen slowly, creating a current. Or it can happen all at once, like lightning or the shock you can get when you touch a doorknob. Two side by side animations illustrate the types of discharges Tim describes. TIM: In fact, capacitors act on the same principle, static electricity! That's when any surface builds up an electric charge, and then discharges. Three animations show a capacitor discharging, a bolt of lightning, and a person getting a shock from touching a doorknob. MOBY: Beep. TIM: In a capacitive touch screen, the discharge never happens. That's what makes them so dang brilliant! MOBY: Beep. TIM: Beneath the glass on your tablet or phone, there's a layer of conductive material. It's so thin that it's transparent, so you can see the display behind it. The layer carries a charge whenever the device is on. The charge generates a field, which projects out from the surface. An animation shows the layer of conductive material that covers a phone's screen, and the layer of glass that sits on top of it. A charge runs through the conductive layer, creating a slightly bulging field as Tim describes. MOBY: Beep. TIM: As you approach the glass, the electric field penetrates your skin. The ions inside your body fluids instantly react. Ions with a like charge are pushed away. Those with an unlike charge are drawn closer. An animation illustrates how the positive ions in a human finger are attracted by the negative field generated by a smartphone's screen. MOBY: Beep. TIM: Right, you create a temporary capacitor at any spot you touch. The glass screen is the insulator, and your finger is the other conductor! Just like in a normal capacitor, the result is an increase in charge. The animation shows the insulator and conductors as Tim describes. An inset image shows the ions and electric field built up in a capacitor. MOBY: Beep. TIM: There are all kinds of ways for it to know exactly where you're touching. In most newer devices, the conductive layer is a series of wires laid one way across the screen, with a series laid the other way below it. An animation shows a smartphone with two conductive layers laid over its screen. The layer closest to the screen contains wires that run vertically. The layer above it contains wires that run horizontally. TIM: Together they form a grid. Wherever you touch can be pinpointed on the grid's coordinates. That goes for multiple touches and motion, too. Tim places his finger on a grid with numbers running vertically and letters running horizontally. The coordinates where he touches the screen read: (3-B) and (1-D). MOBY: Beep. Moby spreads the fingers of both hands apart and examines them. TIM: Oh, right. Most gloves disrupt the electric field coming from your finger. So the touch screen's field won't notice your touch. An animation shows a gloved finger attempting to operate a smartphone's touch screen. The finger has no effect on the electrical field. MOBY: Beep. Moby picks up a display cellphone and prepares to touch its screen. TIM: Oh. Your fingers must be electrically neutral. If they had a charge-- MOBY: Beep. The end of Moby's index finger lights up. TIM: I really wouldn't do that if I were... A laser beam shoots from Moby's finger to the smartphone's screen. The screen melts. The salesperson stands with her hands on her hips, frowning. TIM: Uh, we'll take this one. Category:BrainPOP Transcripts Category:BrainPOP Engineering & Technology Transcripts